1. Field of the Invention
The present invention relates to the production of tablets of sodium dichloroisocyanurate, and more particularly to the production of tablets which dissolve gradually and smoothly in water without causing any undesirable collapse and swelling.
Sodium dichloroisocyanurate is a very useful solid chlorine compound which is effective to release active chlorine for various purposes such as sterilizing water in swimming pools, human waste and sewerage.
2. Description of the Prior Art
Sodium dichloroisocyanurate has been used generally in the form of granules or tablets, but the latter form is more desirable in view of ease in its handling such as in storing, transportation and use.
Various processes have hitherto been proposed for the production of sodium dichloroisocyanurate in tablet form. For instance, Japanese Pat. No. 513 484 (Jap. Pat. Publn. No. 23198/1967) granted to the assignee of the present application, discloses a method wherein sodium dichloroisocyanurate powder is kneaded with sufficient water, the kneaded material with a predetermined water content is tabletted with a surface pressure of about 1000 Kg/cm.sup.2 and then dried. U.S. Pat. Nos. 3,956,444 and 4,024,257 to William Kibbel, Jr. disclose a method wherein sodium dichloroisocyanurate dihydrate is compressed by a surface pressure of from about 2000 to about 10000 p.s.i. to obtain tablets. Further, U.S. Pat. No. 4,261,942 to Tadao SHIMAMURA et al and assigned to the assignee of the present application discloses a method wherein granular sodium dichloroisocyanurate with a moisture content of from 7 to 11 weight % is tabletted.
However, the tablets of sodium dichloroisocyanurate produced by any of such known methods collapse or swell remarkably within a very short time period, when they have been thrown into water, or contacted with sewerage water and the like to be sterilized.
When the conventional tablets are employed as the sterilizer for water, for instance in swimming pools, such phenomena may be advantageous in that the water can rapidly be sterilized within a relatively short time but disadvantageous in that the rapid dissolution of tablets tends to cause an excessive active chlorine concentration in the water, which means an increase of loss of the active chlorine due to rays of the sun and requires a great deal of labor in maintaining and controlling a desired active chlorine level in the water. Further, when the conventional tablets are filled in a cylindrical vessel to sterilize human waste water, the lower end of the vessel is immersed in the water, so that the water rises up in the vessel filled with the tablets due to a capillary action to cause a swelling of the tablets at a level above the water level external to the vessel; this may cause a blocking in the vessel to make impossible a uniform supply of active chlorine to the water being treated.